One use of the term “communion” involves the Mass. We stand with the very first disciples:
158. Like the early communities of Christians, today we gather assiduously to hear the “teaching of the apostles and for the communal life, the breaking of the bread, and to the prayers” (Acts 2:42).
Our communion as a Body, and with the Head is cemented with the proclamation of the Word and the sharing in the Sacrament:
The Church’s communion is nourished with the Bread of God’s Word and with the Bread of the Body of Christ. The Eucharist, sharing of all in the same bread of life and the same chalice of salvation, makes us members of the same body (cf. 1 Cor. 10:17).
Don’t forget Lumen Gentium’s reference to source and summit:
It is the source and culmination of Christian life, (Cf. Lumen Gentium 11) its most perfect expression and food of life in communion. The new gospel relationships that arise from being sons and daughters of the Father and brothers and sisters in Christ are nourished in the Eucharist. The church celebrating is “home and school of communion,” (Novo Millennio Ineunte 43) where the disciples share the same faith, hope, and love at the service of the mission of evangelization.
“School” is something more than an education for the mind. It is also the forerunner of the practice of communion the other days of the week, and not just with other believers in our circles of friends. Communion is also something to be fostered as part of our missionary activity. It’s something in which we are formed (not so much an education).
For deeper examination, an English translation of the 2007 document from the Aparecida Conference.